Harvesting micro algae

ABSTRACT

A reusable composite paramagnetic particle may comprise a paramagnetic core encased by a protective material to which is grafted a tendril layer comprising a plurality of polymeric chains. The polymeric chains may be designed to interact with a microorganism. The interaction between the microorganism and the polymeric chain may be electrostatic. The nanoparticle may be used in a method to isolate or recover microorganisms from solutions using an externally applied magnetic field.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of priority under 35 U.S.C.§119(e) to U.S. provisional application 61/297,533 filed Jan. 22, 2010,the contents of which are hereby incorporated by reference in itsentirety. The present application is related to U.S. provisionalapplication Ser. No. 12/704,416, filed Feb. 11, 2010, titledNANOPARTICLES, COMPOSITIONS THEREOF, AND METHODS OF USE, AND METHODS OFMAKING THE SAME.

BACKGROUND

The subject technology relates generally to devices and methods forisolating microorganisms.

Microorganisms have many commercial applications. Bacteria, fungi, andalgae may be used in various applications for the production ofpharmaceuticals, food, supplements, and even fuel. For example, algaehave applications in pharmaceutical, food, and biofuel production.

Microalgae is a term that may be used to distinguish single-celled,generally microscopic algae from multicellular algae. Algae may be foundin fresh as well as salt water environments.

Use of microalgae in commercial applications may depend in part onunderstanding the biochemical and genetic makeup of microalgae. Inaddition, commercial application may also require cost-effective methodsfor handling microalgae. For example, at present microalgae harvestingtechniques may limit their successful commercialization in theproduction of microalgae-based biofuels.

Some characteristics of microalgae may present challenges for theirefficient harvest. For example, microalgae are generally small (a few toa few hundred micrometers), with low specific gravity, and a generallynegative overall surface charge. In addition, microalgae may grow at lowcell densities in water.

Current techniques used in harvesting microalgae may includecentrifugation, filtration, flotation, flocculation, and ultrasoundsedimentation etc. Each of the present harvesting techniques may havelimitations. For example, centrifugation and ultrasound sedimentationmay be slow processes with concomitantly high operation costs;filtration may be subject to clogging and shortened run times; flotationmay require use of surfactants that may hamper downstream processes; andflocculation may require various chemical additives such as pro-oxidants(to induce liberation of extracellular organic matter), electrolytes(e.g. chitosan), or Al- and Fe-based compounds (to neutralize thesurface charge and aid cell-to-cell adhesion). In addition, some ofthese techniques must be combined for efficient microalgae processing,for example flocculation may also require centrifugation in order tocollect slowly-settled microalgae. Chemicals used in some of these (suchas flocculation or flotation) may inhibit microalgae growth and may bedetrimental for continuous growth-harvest cycled operation.

In some cases, microalgae flocculation has been modeled using theoriesof colloidal stability. For example, the use of polyelectrolyte-inducedflocculation for microalgae harvesting can be understood by DLVO theoryof colloidal stability (DLVO stands for Derjaguin, Landau, Verwey andOverbeek who made seminar contribution to the theory. See: R J Hunter,Foundations of Colloid Science, Clarendon Press, Oxford). DLVO theorymodels flocculation in terms of the interplay between electronic doublelayer repulsion, van der Waals attraction and entropic depletioninteractions.

What is needed is an efficient method of harvesting microorganisms likemicroalgae, that has little or no adverse impact on downstreamprocesses, and that is low-cost.

SUMMARY

The present disclosure is directed to composite particles comprising aparamagnetic core, the core being encased in a coating of a protectivematerial, and the coating grafted to long, polymeric chains designed tointeract with a microorganism.

In various embodiments of the present composite particle theparamagnetic core may comprise iron-oxide, the protective materialcoating may comprise silica, and the polymeric chains may be hydrophilicand/or carry a net charge in aqueous solution.

The size of the paramagnetic core may be between about 1 nanometer toabout 10 micrometers, and may have a protective coating from about 10 nmto about 10 micrometers. The polymeric chains may be generally fromabout 0.1 to about 100 μm (micrometers) in length with a molecular massup to about 10⁷ Daltons (Da).

Methods for using the composite particle are also disclosed. In someembodiments, the particle may be used in harvesting microorganisms froma liquid medium comprising the use of an externally applied magneticfield. In various embodiments the particle may be used in a method ofharvesting microalgae used in biofuel production. In various otherembodiments the particle may be used in a method of harvestingmicroalgae in water treatment. In various other embodiments theparticles may be used in a method of destabilizing colloidal mixtures.

The currently disclosed composite particle may be mass-produced at lowcost and in some embodiments the particle is capable of re-use. In someembodiments the present method may require little or no post-harvestprocessing in order to remove chemicals, reagents, or materials. Invarious other embodiments, the method may involve a de-watering stepwhich may require little maintenance, result in high concentrationfactors, consume little energy, and be operated continuously. Finally inmany embodiments the currently claimed method may have little or noadverse effect on downstream processes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of an embodiment of the presently disclosedcomposite paramagnetic particle.

FIG. 2 depicts the presently disclosed composite paramagnetic particleswith grafted polymers adhering to microalgae.

FIG. 3A depicts rapid precipitation of the present compositeparamagnetic Fe₂O₃ particle device by introduction of an externalmagnetic field. FIG. 3B depicts rapid precipitation of the presentcomposite paramagnetic Fe₃O₄ particle device by introduction of anexternal magnetic field.

FIG. 4 depicts rapid coagulation of microalgae from a rich algal growthmedium by applying a minuscule amount of the present compositeparamagnetic particles (a few milligrams) and a moderate externalmagnetic field (provided by a magnetic stirrer bar).

DETAILED DESCRIPTION

The present disclosure is directed to composite particles comprising aparamagnetic core, the paramagnetic core being encased in a coating of aprotective material, and the coating grafted to long, polymeric chainsdesigned to interact with a microorganism.

In various embodiments of the present composite particle, theparamagnetic core may comprise iron-oxide, the protective coating maycomprise silica, and the polymeric chains may be hydrophilic and/orcarry a net charge in water.

The size of the paramagnetic core may vary from about 1 nanometer toabout 10 micrometers. The thickness of the protective coating may befrom about 10 nm to about 10 micrometers. The polymeric chains may begenerally 0.1 to 100 micrometers in length with a molecular mass fromabout 10¹ to about 10⁷ Daltons (Da).

Methods for using the composite particle as coagulation devices are alsodisclosed. In some embodiments, the particles may be used in harvestingmicroorganisms from a liquid medium involving the use of an externallyapplied magnetic field. In various embodiments the particle may be usedin a method of harvesting microalgae used in biofuel production. Invarious other embodiments the particle may be used in a method ofharvesting microalgae in water treatment. In various other embodimentsthe particle may be used in a method of destabilizing colloidalmixtures.

The currently disclosed composite particle may be mass-produced at lowcost and in some embodiments the particle is capable of re-use. In someembodiments the present method may require little or no post-harvestprocessing to remove chemicals, reagents, or materials. In various otherembodiments, the method may involve a de-watering step which may be oflow maintenance, result in high concentration factors, consume littleenergy, and be operated continuously. Finally in many embodiments thecurrently claimed method may have little or no adverse effect ondownstream processes.

As depicted in FIG. 1, the presently disclosed composite paramagneticparticle may comprise three general layers: (1) a core; (2) a protectivecoat or shell which encases the core; and (3) a tendril layer comprisingpolymer chains grafted on, to, or from the protective coating.

In various embodiments the paramagnetic core may comprise a γ-Fe₂O₃. Theiron oxide allows the core to exhibit magnetism in response to anexternally applied magnetic field, while exhibiting little or nomagnetism in the absence of an external magnetic field. In variousembodiments the core may comprise Fe₃O₄. In other embodiments the coremay comprise other paramagnetic particles comprising, for example, Co,CoPt, CoO, CoFe₂O₄, Fe, FePt, Ni etc.

The protective shell may help prevent leaching of the paramagneticmaterial out of the core as well as create a surface for attachment orgrafting of polymeric chains. The protective coating may also aid inimparting wettability to the particle.

In various embodiments the protective coating material may be silica. Asilica shell may help provide a rich chemistry (silane chemistry) formodifying the surface of the particle.

The tendril layer may aid in interacting with microorganisms. Thetendril layer may also help improve the dispersion of compositeparticles. The polymeric chains of the tendril layer may help promoteaggregation of microorganisms. The polymeric chains may be designed tointeract with microorganisms in various ways, for example throughelectrostatic interactions, van der Waals forces, and entropic depletioneffects. In further embodiments the interactions may involve acombination of various forces.

In various embodiments, composite paramagnetic particles may be added toa solution containing a microorganism. The polymeric chains of theparticles may interact with microorganisms within the solution. Acomposite paramagnetic particle may have multiple polymeric chains whichmay allow an individual particle to aggregate several microorganisms.After allowing the composite particles and microorganisms to interact,an external magnetic field may be applied. The application of anexternal magnetic field may result in attracting the paramagnetic coreto the magnetic source. This attraction may result in concentrationand/or precipitation of the microorganism.

The presently disclosed composite particles may be used to rapidlyprecipitate microorganisms from various solutions. In some embodimentsthe microorganism solution may be less than 10 liters. In otherembodiments the microorganism solution may be greater than 10 liters. Insome embodiments the composite particle may be used to continuouslyharvest microorganisms.

The presently disclosed composite particles may cause little or noadverse interference to common processing steps performed onmicroorganisms. For example, the disclosed composite particle may beused in lipid extraction methods, solvent extraction, mechanical press,and/or supercritical water extraction. Additionally, the particle may beused to recover microorganisms from solution without additionalmechanical or chemical processing. After elution of the microorganismfrom the composite particle, the composite particle may be re-collectedby magnetic force and re-used.

The choice of particle sizes, volume fractions, polymer chain length,compositions and charge states may be varied to optimize efficientharvesting of various target microorganisms.

Paramagnetic Core

Paramagnetic refers to substances that may exhibit magnetism in responseto an external magnetic force. Paramagnetic substances generally do notexhibit magnetism in the absence of an externally applied magneticforce.

A wide variety of methods have been reported for making paramagneticparticles. For instance, paramagnetic γ-Fe₂O₃ particles can be preparedby injecting Fe(CO)₅ into a hot surfactant mixture of octyl ether andoleic acid (see descriptions in: Hyeon T et al, J. Am. Chem. Soc., 2001,123, 12798-12801), and paramagnetic Fe₃O₄ particles can be prepared byan autoclave reaction of FeCl₃, ethylene glycol, NaAc, and polyethyleneglycol mixture solution (see descriptions in: Deng H et al, Angew. Chem.Int. Ed. 2005, 44, 2782-2785). Preparation of other paramagneticparticles are also well documented (see for example: Jeong U et al, Adv.Mater. 2007, 19, 33-60 and references therein).

The composite particle may comprise a generally paramagnetic core.Various materials may be used to construct the paramagnetic core of thecomposite particle device. In some embodiments, the core material maycomprise iron oxide. The magnetic core may also comprise other metaloxides such as Co. In further embodiments, the magnetic core may alsoinclude non-metal oxide materials like Co, CoPt, Fe, FePt, Ni etc. maybe used. Further, those skilled in the art will recognize that differentmaterials may be combined in the manufacture of these particles.

The paramagnetic core as described herein is generally between about 1nanometer and about 10 micrometers in size. The paramagnetic core mayhave various shapes, including rods, spheres, and platelets.

In various embodiments, the paramagnetic core may measure greater than30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm,130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm,220 nm, 230 nm, or 240 nm in at least one measureable dimension. Inother embodiments, particles may measure less than 250 nm, 240 nm, 230nm, 220 nm, 210 nm, 200 nm, 190 nm, 180 nm, 170 nm, 160 nm, 150 nm, 140nm, 130 nm, 120 nm, 110 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm,or 40 nm in at least one measurable dimension.

Protective Coating of Paramagnetic Core

In various embodiments, the paramagnetic core may be coated with aprotective material. The protective material may help to encase theparamagnetic material of the core and may also provide a surface forattachment and/or grafting of polymeric chains.

The protective material may create a shell of variable thickness. Insome embodiments, the shell may be about 100 nm. In other embodimentsthe protective shell may be generally less than 100 nm thick. In otherembodiments the shell may be generally greater than 100 nm thick.

In various embodiments the material used to coat the paramagnetic corescomprises silica. Silanization of the particle may help create afunctional coating for grafting or attaching polymer chains to thenanoparticle. Alternative embodiments may use non-silica materials,including but not limited to polymeric film, carbon, carbon nitride,boron nitride etc.

In various embodiments, silanization may include preparing a functionalsilane solution using anhydrous solvents and adding paramagnetic corematerial to the silane solution, followed by allowing the solution toreact then washing and drying the particles. In other embodiments,silanization may include the use of reverse microemulsion where theparamagnetic cores are dispersed in a water-in-surfactant reversemicroemulsion, and hydrolyzation of alkyl silane leads to the formationof silica coating around the paramagnetic core (see for example: Yi D Ket al, Chem. Mater., 2006, 18, 614-619). In some embodiments thefunctional silanes may have a generic form of R¹ _(x)—Si—(OR²)_(4-x),where x is 1, 2, or 3, R² is usually an alkyl-group, R¹ is an alkylchain with a functional moiety as the end group. In some embodiments thefunctional moiety may be alkyl, alkene, alkyne, aryl, azide, hydroxyl,carboxyl, amine, amino, thio, epoxy, cyano, or halogen.

The protective coating may be modified prior to the graft-to orgraft-from polymerization methods to aid in covalently bonding a varietyof polymers with controllable chain length to the coating. For example,a silica coat may be modified, for instance, by(3-Aminopropyl)triethoxysilane or 5,6-Epoxyhexyltriethoxysilane, andanchored with RAFT (reversible addition-fragmentation chain transfer)functionalities. This modification may allow for “controlled/livingpolymerization” of grafted polymers (an example is as described in“Functional polymers from novel carboxyl-terminated trithiocarbonates ashighly efficient RAFT agents” by Lai, J. T.; Filla, D.; Shea, R.,Macromolecules 2002, 35, 6754-6756). Controlled/living polymerizationdescribes polymerization in which termination of a growing polymer chainis inhibited, and the polymer chain may grow until monomers are consumedafter which polymerization may again continue if new monomers are addedto the reaction. RAFT is one example of controlled/livingpolymerization.

Polymeric Chain

In various embodiments, the outmost layer of the disclosed compositeparticles is comprised of grafted polymer chains. The polymeric chainlength may be varied to aid in interacting with a target microorganism.In various embodiments the polymeric chains may vary from about 0.1 μmand about 100 μm. In various embodiments the polymeric chains may beless than 0.1 μm in length. In various embodiments the polymer chainlength may be greater than 100 μm.

Polymeric chains may vary in molecular mass from about 1 kDa to about10,000 kDa. In various embodiments the polymeric chains may be less than1 kDa. In various embodiments the polymeric chains may be greater than10,000 kDa.

In various embodiments the polymers are comprised of subunits that arehydrophilic. In some embodiments the polymer chain may be comprised ofsubunits that are generally negatively charged. In other embodiments thepolymer chain may be comprised of subunits that are generally positivelycharged. In various other embodiments the polymeric subunits comprisingthe polymer chain may be neutral, negatively charged, and/or positivelycharged. In other embodiments the polymeric subunits may be chosen toselect a generally uniform or non-uniformly charged polymer chain. Invarious embodiments the polymer chain may be neutral.

In various embodiments the number of polymeric chains per compositeparamagnetic particle is between about 5 and about 20 chains. In variousembodiments individual particles may have less than about 5 chains. Invarious other embodiments individual nanoparticles may have more than 20polymeric chains.

The polymeric chains may be generally flexible to aid in interactingwith target microorganisms.

In various embodiments the polymer chain may be generally cationic. Inthose embodiments the polymers include, but are not limited to,chitosan, poly (N-ethyl-4-vinypyridinium), poly(2,2-(dimethyl aminoethylmethacrylate), poly(ethylene imine), poly(allylamine), and poly(diallyldimethyl ammonium chloride) etc.; In various embodiments the polymerchain may be generally anionic. In those embodiments the polymersinclude, but are not limited to, poly(acrylic acid), poly(styrenesulfonate), poly(vinyl sulfate), and poly(3-sulfopropyl methacrylate)etc.; In various other embodiments the polymer chain may be generallyhydrophilic and neutral. In those embodiments the polymers include, butare not limited to, polyethylene glycol, poly(2-methyloxazoline,poly(2-ethyl-2-oxazoline), and polyacrylic amide etc.

The polymeric chains may be generally homogeneous on an individualcomposite particle, that is all chains on a composite paramagneticparticle may be substantially similar in length, weight, composition,charge, etc. In various other embodiments the polymeric chains on anindividual composite particle may vary, that is, various chains on anindividual particle may differ in length, mass, composition, and/orcharge etc.

Various methods are available to elute microorganisms from the compositeparamagnetic particles after recovery of the microorganism. For example,elution may be achieved by treating the composite particle-boundmicroorganism with a high or low ionic strength solution, organicsolvent and/or ionic liquid extraction, and/or supercritical watertreatment etc.

Polymerization

In various embodiments the grafted polymer chains are formed bystep-growth or chain-growth polymerization. Step growth may be referredto polymerization that occurs in a stepwise fashion, for examplemonomer->dimer->trimer->etc. This type of polymerization may involvereaction of functional groups between monomers (such as —OH and —COOH)and as a result, the molar mass increases slowly. Chain grown may referto a fast linkage of monomers by initiation (activate the unsaturatedbonds). During chain growth, the molar mass may increase rapidly. Insome embodiments the polymerization process occurs as controlled/livingpolymerization, such as for example RAFT polymerization.Controlled/living polymerization describes polymerization in whichtermination of a growing polymer chain is inhibited, and the polymerchain may grow until monomers are consumed after which polymerizationagain continue if new monomers are added to the reaction. RAFT is oneexample of living polymerization.

RAFT polymerization operates on the principle of degenerative chaintransfer (see review: Moad G et al, Aust. J. Chem., 2005, 58, 379-410).Without being limited to a particular mechanism, Scheme 1 shows aproposed mechanism for RAFT polymerization. In Scheme 1, RAFTpolymerization involves a single- or multi-functional chain transferagent (CTA), such as the compound of formula (I), includingdithioesters, trithiocarbonates, xanthates, and dithiocarbamates. Theinitiator produces a free radical, which subsequently reacts with apolymerizable monomer. The monomer radical reacts with other monomersand propagates to form a chain, Pn*, which can react with the CTA. TheCTA can fragment, either forming R*, which will react with anothermonomer that will form a new chain Pm* or Pn*, which will continue topropagate. In theory, propagation to the Pm* and Pn* will continue untilno monomer is left or a termination step occurs. After the firstpolymerization has finished, in particular circumstances, a secondmonomer can be added to the system to form a block copolymer.

RAFT polymerization involves a similar mechanism as traditional freeradical polymerization systems, with the difference of a purposely addedCTA. Addition of a growing chain to a macro-CTA yields an intermediateradical, which can fragment to either the initial reactants or a newactive chain. With a high chain transfer constant and the addition of ahigh concentration of CTA relative to conventional initiator, synthesisof polymer with a high degree of chain-end functionality and with welldefined molecular weight properties is obtained.

RAFT polymerization may be used in the synthesis of multifunctionalpolymers due to the versatility of monomer selection and polymerizationconditions, along with the ability to produce well-defined, narrowpolydispersity polymers with both simple and complex architectures.

In particular embodiments, RAFT polymerization is used to produce avariety of well-defined, novel biocopolymers as constructs formultifunctional systems for the surface modification of disclosedcomposite particles consisting of a paramagnetic core encased in aprotective coating. The inherent flexibility of RAFT polymerizationsmakes it a candidate to produce well-defined polymer structures.

In various embodiments, the polymerization process is Atom TransferRadical Polymerization (“ATRP”) ATRP is an example of controlled/livingradical polymerization. In some embodiments, ATRP employs atom transferfrom an organic halide to transition-metal complex to generate thereacting radicals, followed by back transfer from the transition metalto a product radical to form the final polymer product. One example ofATRP may be found in, Patten T E, Matyjaszewski K, “Atom TransferRadical Polymerization and the Synthesis of Polymeric Materials”, whichis incorporated herein in its entirety. (Adv. Mater., 1998, 10,901-915).

In various embodiments, the polymerization process is ring-openingpolymerization. Ring-opening polymerization is a form of chain-growthpolymerization, in which the terminal end of a polymer acts as areactive center, where further cyclic monomers join to form a largerpolymer chain through ionic propagation. One example of ring-openingpolymerization may be found in, Dechy-Cabaret O et al, “Controlledring-opening polymerization of lactide and glycolide”, which isincorporated herein in its entirety. (Chem. Rev., 2004, 104, 6147-6176).

In various embodiments, the polymerization process is anionicpolymerization. Anionic polymerization is a form of chain-growthpolymerization that involves the polymerization of vinyl monomers withstrong electronegative groups. One example of anionic polymerization maybe found in Hsieh H and Quirk R “Anionic Polymerization: Principles andpractical applications”, which is incorporated by reference in itsentirety. (Marcel Dekker, Inc: New York, 1996);

In various embodiments, the polymerization process is cationicpolymerization. Cationic polymerization is a type of chain growthpolymerization in which a cationic initiator molecule binds andtransfers charge to a monomeric unit, which becomes reactive as a resultand reacts similarly with other monomeric units to form a polymer. Oneexample of cationic polymerization may be found in Odian G, “Principlesof Polymerization”, which is incorporated by reference in its entirety.(Wiley-Interscience, Hoboken, N.J., 2004)

In certain aspects, pre-formed polymers may be grafted to the protectivecoating instead of the graft-from polymerization on the protectivecoating.

Flocculation

Inter-particle forces, as well as hydrodynamics, and solution conditions(pH, ion strength, etc.) may aid in the harvesting of microalgae fromsolutions. For example, DLVO flocculation theory posits thatidentifiable distances may exist (primary and secondary minima) at whichthe forces of attraction may exceed those of electrostatic repulsionwhich may result in adhesion. DLVO theory may be used to model thepresent interaction between microalgae and the currently disclosedcomposite particle device.

Some studies in colloidal science have recently revealed that extremelylow nanoparticle volume fractions (<10⁻⁵) could be used to stabilize orflocculate colloidal suspensions depending on the nature ofcolloid-nanoparticle interactions (see: Tohver, V. et al, Proc. Natl.Acad. Sci. U.S.A., 2001, 98, 8950-8954).

In various embodiments the composite particles may be added to asolution containing microorganisms and allowed to interact. In variousembodiments the solution may be stirred to help facilitate interactionbetween the composite particles and microorganisms.

EXAMPLES Example 1

The presently disclosed γ-Fe₂O₃@SiO₂ composite particles may be welldispersed in solution. FIG. 3A, at left shows a solution of silicacoated Fe-oxide nanoparticles in solution. The photo at right in FIG. 3Ashows the solution shortly after introduction of an external magneticfield. This figure demonstrates that a homogeneous solution of thepresent composite particle devices may be rapidly, efficiently, andinexpensively concentrated. The presently disclosed composite particlescan be precipitated out of solution rapidly under magnetic field (FIG.3A). FIG. 3B depicts similar results using Fe₃O₄ particles.

Example 2

The presently disclosed γ-Fe₂O₃@SiO₂@Polymer composite particles areused as coagulation agents to rapidly and efficiently concentratemicroalgae from growth medium under external magnetic field (H), asschematically depicted in FIG. 2. The composite particles are able to bere-used after microalgae elution or biofuel extraction, thus greatlyreduce the cost.

Example 3

Fe₃O₄@SiO₂@Polymer composite particles were used as coagulation agentsto rapidly and efficiently concentrate microalgae from a rich algalgrowth medium. A moderate external magnetic field (H) was provided by amagnetic stirrer bar. The microalgal strain used was Nannochloropsis,which has a small diameter (˜2 μm) and low specific density due to highoil content (˜50% by dry weight). Nannochloropsis is extremely hard toharvest via conventional methods. FIG. 4 shows nearly 100% coagulationof Nannochloropsis occurs in a few seconds after adding a few milligramsof the presently disclosed Fe₃O₄@SiO₂@Polymer composite particles(right: before coagulation; left: after coagulation).

All directional references (e.g., upper, lower, upward, downward, left,right, leftward, rightward, top, bottom, above, below, inner, outer,vertical, horizontal, clockwise, and counterclockwise) are only used foridentification purposes to aid the reader's understanding of the exampleof the invention, and do not create limitations, particularly as to theposition, orientation, or use of the invention unless specifically setforth in the claims. Joinder references (e.g., attached, coupled,connected, joined, and the like) are to be construed broadly and mayinclude intermediate members between a connection of elements andrelative movement between elements. As such, joinder references do notnecessarily infer that two elements are directly connected and in fixedrelation to each other.

In some instances, components are described with reference to “ends”having a particular characteristic and/or being connected with anotherpart. However, those skilled in the art will recognize that the presentinvention is not limited to components which terminate immediatelybeyond their points of connection with other parts. Thus, the term “end”should be interpreted broadly, in a manner that includes areas adjacent,rearward, forward of, or otherwise near the terminus of a particularelement, link, component, part, member or the like. In methodologiesdirectly or indirectly set forth herein, various steps and operationsare described in one possible order of operation, but those skilled inthe art will recognize that steps and operations may be rearranged,replaced, or eliminated without necessarily departing from the spiritand scope of the present invention. It is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative only and not limiting. Changes indetail or structure may be made without departing from the spirit of theinvention as defined in the appended claims.

It will be apparent to those of ordinary skill in the art thatvariations and alternative embodiments may be made given the foregoingdescription. Such variations and alternative embodiments are accordinglyconsidered within the scope of the present invention.

1. A composite particle comprising: a core; a protective shell encasingsaid core; and a tendril layer, further comprising a plurality ofpolymeric chains attached to the protective shell.
 2. The compositeparticle of claim 1, wherein the core further comprises a paramagneticmaterial.
 3. The composite particle of claim 2, wherein the paramagneticmaterial comprises iron oxide.
 4. The composite particle of claim 3,wherein the core material comprises Fe₂O₃.
 5. The composite particle ofclaim 3, wherein the core material comprises Fe₃O₄.
 6. The compositeparticle of claim 1, wherein the protective shell comprises silica. 7.The composite particle of claim 1, wherein the polymeric chains arehydrophilic.
 8. The composite particle of claim 7, wherein the polymericchains have a net positive charge.
 9. The composite particle of claim 7,wherein the polymeric chains have a net negative charge.
 10. Thecomposite particle of claim 7, wherein the polymeric chains have no netcharge.
 11. A method of recovering a microorganism from a solutioncomprising: providing a microorganism in a solution; adding a compositeparamagnetic particle, wherein the composite particle has a silicaencased iron oxide core, and polymeric chains grafted to the silica;allowing the composite particles to be suspended in the solution;waiting sufficient time to allow the composite particles andmicroorganisms to interact; applying an external magnetic field to thesolution; and recovering the composite particles and microorganismsuspension.
 12. The method of claim 11, wherein the microorganism ismicroalgae.
 13. The method of claim 11, wherein the solution is drinkingwater.
 14. The method of claim 12, wherein the microalgae are producingbiofuels.
 15. The method of claim 11, wherein the composite particlesare reused particles.
 16. A composite particle comprising: a crystallineiron oxide core, a silica shell coating the core; and a tendril layercomprising a plurality of polymeric chains, wherein the polymeric chainsare grafted to or grafted from the silica shell.
 17. The particle ofclaim 16, wherein the polymeric chains are grafted onto the silica shellby one or more of step-growth polymerization, chain-growthpolymerization, and controlled/living polymerization.
 18. The method ofclaim 17, wherein the “controlled/living” polymerization method is oneor more of reversible addition fragmentation transfer polymerization,atom transfer radical polymerization, ring-opening polymerization,anionic polymerization and cationic polymerization.
 19. The particle ofclaim 16, wherein the polymeric chains are grafted onto the silica shellby reversible addition fragmentation transfer polymerization.
 20. Theparticle of claim 19, wherein the silica coating is modified by3-Aminopropyltriethoxysilane or 5,6-Epoxyhexyltriethoxysilane prior tografting the polymeric chains.